[Ghost1063]

Overview

This PR adds a typed account lookup boundary so SEP-10 authentication can read configured account signers, weights, and thresholds instead of requiring the account master key. The lookup returns distinct not-found and upstream-error outcomes, and the HTTP handling in the Express router now distinguishes them.

Related Issue

Closes #AK-028

Changes

• [MODIFY] src/runtime/interfaces.ts

  • Adds the typed account lookup interface returning signer keys, weights, and thresholds, with separate not-found and upstream-error result variants.

• [MODIFY] src/runtime/http/express-router-impl.ts

  • Injects the account lookup and maps not-found and upstream-error outcomes to distinct HTTP responses.

• [MODIFY] src/runtime/http/express-router.ts

  • Passes the injectable lookup through the router factory.

• [MODIFY] src/services/stellar-signer.ts

  • Reads account signers and thresholds through the lookup boundary for signature verification.

Verification Results

Focused check (fixtures for existing, nonexistent, and unavailable accounts; no real credentials):

npm test -- src/runtime/http

Expected result: the existing-account, nonexistent-account, and unavailable-account cases pass, with not-found and upstream-error responses asserted as distinct.

Type and build checks:

npx tsc --noEmit
npm run lint
npm run build

Acceptance Criteria	Status
Tests provide existing, nonexistent and unavailable accounts without real credentials	✅ Fixture-based lookup doubles
HTTP handling distinguishes those outcomes	✅ Distinct not-found and upstream-error responses
Reproducible focused check with command and expected result documented	✅ npm test -- src/runtime/http

Closes #704